JP2014072327A - Photoelectric conversion element consisting of organic inorganic hybrid structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solar cell consisting of a solid thin film organic inorganic hybrid structure in which fill factor (FF) and photoelectric conversion efficiency are improved.SOLUTION: A photoelectric conversion element is obtained by laminating a metal oxide semiconductor having a nano porous structure, a photosensitive material having a perovskite crystal structure represented by a general formula CHNHMX(In the formula, M1 is a bivalent metallic ion, X is F, Cl, Br, I), and a thin layer of a conductive material composed of nanotubes, sequentially on a conductive substrate. A perovskite crystal material of organic inorganic composite semiconductor material is applied, and carbon nanotubes having excellent conductivity is combined, as a charge transport layer, with strong light absorption and high efficiency photocharge separation function of the composite material.

Description

  The present invention relates to a thin film solar cell having an organic-inorganic hybrid structure produced by chemically combining an inorganic compound and an organic compound.

  Organic solar cells using organic compounds as power generation materials or conductive materials are applied to physical junction solar cells that use inorganic materials such as silicon crystals, silicon thin films, and copper / indium / selenium junctions (CIS type). Development research is active because it can be produced at low cost using technologies and has features such as high sensitivity response to light with low illuminance and high voltage output. Among these, dye-sensitized solar cells use a dye-sensitized semiconductor made by adsorbing a dye on a metal oxide semiconductor as a photoelectrode for photovoltaic power generation, and a liquid electrolyte containing a redox compound is joined to this. The solid-liquid interface is a wet-type electrochemical cell related to the principle of power generation, is easy to manufacture, and is known to provide a light energy conversion efficiency of 11% or more that exceeds that of a thin-film silicon solar cell (Non-Patent Document 1). ). On the other hand, the structure and principle of organic thin-film solar cells are significantly different from those of dye-sensitized solar cells. The solid-solid physical junction of organic materials is used as a thin film for photovoltaic power generation. An interface formed by a junction of an n-type (electron donor) and a p-type (electron acceptor) of an organic material that is close to a junction solar cell and has photosensitivity or charge transport capability is involved in the principle of power generation (Non-patent Document 2). .

  Dye-sensitized solar cells and organic thin-film solar cells share the same point that the materials involved in light absorption are organic compounds. However, since the junction structure and the principle of power generation are different, the characteristics and durability of photovoltaic power generation are different. There is a tendency for sex to vary greatly. As an organic solar cell in the middle of these two types of solar cells, there is a solid type dye-sensitized solar cell in which a liquid electrolyte containing a redox compound is replaced with a solid inorganic material or organic material capable of charge transport. It has been studied (Non-Patent Document 3). However, the performance of the solid dye-sensitized solar cell has not reached the performance of the conventional liquid dye-sensitized solar cell. On the other hand, an organic thin-film solar cell having an all-solid structure in which a semiconductor thin film such as titanium oxide is inserted into a laminated structure for the purpose of rectifying electron transfer in the structure of the organic thin-film solar cell has been tried (Non-Patent Document). 2). However, thin film solar cells using these organic materials are subject to further improvement in that the high internal resistance resulting from the low conductivity inherent in organic materials leads to a decrease in output.

  As for photosensitive materials used for organic solar cells, that is, materials responsible for photoelectric response, organic light-emitting solar cells generally include visible light-sensitive organic materials such as polyphenylene vinylene, polythiophenes, phthalocyanines, and benzoporphyrins. It is typically used and its types are limited. In contrast, in dye-sensitized solar cells, various kinds of organic materials and inorganic materials are used as photosensitive sensitizers. In organic materials, in addition to typical ruthenium complex dyes, metal porphyrins are used. Metal phthalocyanines, metal-free indoline-based and oxazole-based organic dyes, and polymer materials such as polythiophene are used. As inorganic materials, quantum dots represented by CdS, CdSe, and PdS have been studied as sensitizers. More recently, a crystal material having a perovskite structure as an organic-inorganic composite compound has been used as a visible light sensitizer, and a relatively high voltage and efficiency have been obtained (Non-patent Document 4).

  As a charge transport material that mediates electronic conduction to the photosensitive material, in a dye-sensitized solar cell, an electrolytic solution containing a redox agent such as iodine ion is generally used. On the other hand, solid-state dye-sensitized solar cells that do not use an electrolyte solution have been studied, and a method using a material having a hole transport function typified by SpiroOMeTAD as an organic compound instead of the electrolyte solution is known. (Non-Patent Document 5). As an inorganic compound, a method using p-type inorganic compound semiconductor particles such as CuII has been known for a long time, and recently, a method using a perovskite compound such as a structure of CsSnI3 as a hole transporting agent has been disclosed. (Non-Patent Document 6). However, these organic and inorganic solid charge transport materials are liquids in terms of electrical conductivity due to the low conductivity inherent in organic materials and the large contact resistance with the surface of the semiconductor porous film. It is not sufficient compared with the electrolytic solution, and the internal resistance of the cell is increased, and the reduction of the fill factor (FF), which is a resistance factor, often causes a decrease in efficiency.

  The organic solar cells described above have a cell internal resistance at the time of photovoltaic power generation, compared to conventional solid junction solar cells such as silicon, due to the type of photosensitive material or charge transport material constituting the solar cell. High is a common drawback, which results in a low value of the fill factor (FF), which is the resistance factor of the cell, resulting in a decrease in energy conversion efficiency. This problem is particularly noticeable when the density of the photocurrent increases under a strong light amount. As a result of the increase in IR loss, the FF decreases and the conversion efficiency decreases. Therefore, in order to improve the performance of an organic solar cell, it is necessary to design a structure that reduces the internal resistance of the cell while reducing the amount of organic material that causes high resistance.

Supervised by Tsutomu Miyasaka, New concept solar cell and manufacturing process, CMC Publishing, 2009 Supervised by Satoshi Uehara and Satoshi Yoshikawa, Latest Technology II for Organic Thin-Film Solar Cells, CMC Publishing, 2009 A. Konno, G. R. A. Kumara, S. Kaneko, B. Onwona-Agyeman, K. Tenennakone, Chemistry Letters, 2007, 36, p716-717. A. Kojima, K. Teshima, Y. Shirai, and T. Miyasaka, Journal of American Chemical Society, 2009, 131, p6050-6051. I. K. Ding, N. Tetreault, J. Brillet, B. E. Hardin, E. H. Smith, S.J. Rosenthal, F. Sauvage, M. Graetzel, and M. D. I. Chung, B. Lee, J. He, R. P. H. Chang, and M. G. Kanatzidis, Nature, 2012, 485, p486-489.

In organic solar cells that use organic materials as either photosensitive materials or charge transport materials, internal resistance is generally high, especially in solid-state dye-sensitized solar cells that use solid organic materials as charge transport materials. A decrease in fill factor (FF) and conversion efficiency due to increased resistance tends to limit the range of solar cell performance.
Accordingly, the present invention applies a perovskite crystal material, which is an organic-inorganic composite semiconductor material, to the photosensitive material, and has a strong light absorption and high-efficiency photocharge separation function, and carbon having excellent conductivity. An object of the present invention is to provide a solar cell having a solid thin film type organic-inorganic hybrid structure with improved fill factor (FF) and photoelectric conversion efficiency by combining nanotubes as a charge transport layer.

The present invention can solve the above problems in the following aspects (1) to (5).
(Aspect 1) A metal oxide semiconductor having a nanoporous structure on a conductive substrate, a general formula CH ₃ NH ₃ M ¹ X ₃ (wherein M ¹ is a divalent metal ion, X is F , Cl, Br, and I)), and a thin layer of a conductive material made of carbon nanotubes is sequentially stacked, and a photoelectric conversion element having a perovskite crystal structure.

(Aspect 2) The aspect (Aspect 1) is characterized in that the thin layer of the conductive material made of carbon nanotubes is a conductive organic compound containing carbon nanotubes in a range of 5% to 50% by weight. It is a photoelectric conversion element. A thin film having a carbon nanotube content of less than 5% by weight is insufficient in conductivity, and the performance of photoelectric conversion is lowered due to an increase in internal resistance. In a thin film in which the content of carbon nanotubes exceeds 50% by weight, the carbon nanotubes cause aggregation in the organic compound, resulting in a non-uniform thin film, resulting in a problem that current rectification deteriorates and photoelectric conversion performance deteriorates.

(Aspect 3) The aspect (Aspect 1) is characterized in that the thin layer of the conductive material made of carbon nanotubes is a conductive inorganic compound containing carbon nanotubes in a range of 5% to 50% by weight. It is a photoelectric conversion element. A thin film having a carbon nanotube content of less than 5% by weight is insufficient in conductivity, and the performance of photoelectric conversion is lowered due to an increase in internal resistance. In a thin film in which the content of carbon nanotubes exceeds 50% by weight, there is a problem that the conductive inorganic compound is poorly filled into the metal oxide having a nanoporous structure, and the performance of photoelectric conversion is deteriorated.

(Aspect 4) In the above (Aspect 1) or (Aspect 2), the conductive organic compound further includes a photosensitive organic compound having light absorption in a wavelength range of 400 nm to 1500 nm. It is a photoelectric conversion element to describe. Many perovskite photosensitive materials have a light absorption wavelength that is limited to the visible wavelength range, so the ability to absorb light (condensation) can be achieved by adding organic compounds that absorb light from visible light to infrared light. To increase the efficiency of the photoelectric conversion element. In particular, it is more preferable to include a photosensitive organic compound having light absorption in a wavelength range of 600 nm to 1500 nm.

(Aspect 5) The aspect described in (Aspect 1) or (Aspect 3) is characterized in that the conductive inorganic compound is a p-type inorganic semiconductor having light absorption in a wavelength range of 400 nm to 1500 nm. It is a photoelectric conversion element. Since many of the perovskite photosensitive materials have a light absorption wavelength limited to the visible light wavelength region, light absorption (condensation) can be achieved by adding a p-type inorganic semiconductor that absorbs light from visible light to infrared light. The efficiency of the photoelectric conversion element is increased by improving the conductivity utilizing the hole transport capability of the p-type inorganic semiconductor. In particular, it is more preferable to include a photosensitive inorganic semiconductor having light absorption in a wavelength range of 600 nm to 1500 nm.

  According to the photoelectric conversion element having an organic-inorganic laminated structure including the carbon nanotube, a perovskite material as a photosensitive material and a carbon nanotube as a charge transport material can be formed on an electrode in a short time by applying a simple solution. A thin-film solid-type solar cell having excellent photoelectric conversion characteristics can be manufactured by a low-cost process.

It is sectional drawing which shows schematic structure of the photoelectric conversion element which concerns on Embodiment 1 of this invention.

Hereinafter, the configuration of the photoelectric conversion element (organic thin-film solar cell) according to Embodiment 1 of the present invention and the manufacturing method thereof will be described.
As shown in FIG. 1, the photoelectric conversion element of the present invention comprises a transparent electrode 1, a counter electrode 2, and a photosensitive material having a perovskite crystal structure between these electrodes (1, 2) (hereinafter referred to as “photosensitive”). The power generation layer 3 made of the metal oxide semiconductor porous film 31 covered with 32 and the charge transport layer 4 made of carbon nanotubes are sequentially laminated. The transparent electrode 1 is composed of a transparent substrate 11 and a transparent conductive film 12 formed (arranged) on the surface of the transparent substrate 11, and a buffer layer 5 is provided on the surface of the transparent conductive film 12 to cover it. . The counter electrode 2 is composed of a conductive metal thin film or a thin film containing a conductive oxide.

  For the transparent substrate 11, a synthetic resin plate, a glass plate, or the like is appropriately used. As the synthetic resin plate, thermoplastic resin such as polyethylene naphthalate (PEN) film, polyethylene terephthalate (PET), polyester, polycarbonate, polyolefin, polyimide, Teflon (registered trademark), etc. are used.

As the transparent conductive film 12, tin-added indium oxide (ITO), fluorine-added tin oxide (FTO), or a laminated film thereof is used. In addition, tin oxide (SnO ₂ ), indium zinc oxide (IZO), A thin film containing a conductive metal oxide such as zinc oxide (ZnO) can be used. In addition, a thin film of a polymer material having high conductivity can be used. As such a polymer, for example, a polyacetylene-based, polypyrrole-based, polythiophene-based, or polyphenylene vinylene-based polymer is selected. The surface resistance of these transparent conductive films is preferably 15Ω / □ or less, and more preferably 5Ω / □ or less.

Examples of the counter electrode 2 include metals such as aluminum, gold, silver, and platinum, tin-added indium oxide (ITO), fluorine-added tin oxide (FTO), tin oxide (SnO ₂ ), indium zinc oxide (IZO), An organic conductive material containing a conductive metal oxide such as zinc oxide (ZnO), a conductive polymer, or the like is used. These are formed as a thin film by vapor deposition or sputtering, or those coated with a dispersion containing these materials by coating. The counter electrode 2 may be a solid substrate made of the above metal, metal oxide thin film, carbon material, or the like.

The metal oxide semiconductor porous film 31 includes oxides of metals such as titanium, tin, zinc, iron, tungsten, zirconium, strontium, indium, cerium, yttrium, lanthanum, vanadium, niobium or tantalum as oxide semiconductors. Is used. Preferably, metal oxides such as titanium oxide (TiO ₂ ), titanium strontium oxide (TiSrO ₃ ), zinc oxide (ZnO), tin oxide (SnO ₂ ), tungsten oxide (WO ₃ ), niobium oxide (Nb ₂ O ₅ ), etc. In particular, titanium oxide (TiO ₂ ), titanium strontium oxide (TiSrO ₃ ), and zinc oxide (ZnO) are preferably used. Two or more of these oxide semiconductors may be combined to be used as a semiconductor porous layer. The semiconductor porous layer is prepared by preparing a viscous colloid or paste prepared by dispersing the above-described oxide semiconductor nanoparticles or a precursor thereof in a solvent, and applying the viscous dispersion to a substrate. By baking, it can be obtained as a solid thin film. Such a solid thin film provides an optically translucent feature due to the porosity created by the nanoparticles.

  A buffer layer 5 that covers the transparent conductive film of the transparent electrode is provided below the metal oxide semiconductor porous film 31. The buffer layer separates the charge transport layer and the transparent conductive film and serves to prevent electrical contact between them. The buffer layer is a transparent conductive material having a dense structure having no pores, and is preferably an organic or inorganic n-type semiconductor. Preferred as the buffer layer is a metal oxide, such as titanium oxide, zinc oxide, niobium oxide, and zirconium oxide. The thickness of the buffer layer is preferably 10 nm or more and 200 nm or less, and particularly preferably 10 nm or more and 70 nm or less.

The metal oxide porous semiconductor film used in the solar cell of the present invention is a thin film having a specific surface area of 20 (m ² / g) or more, and the thickness of the thin film is from 100 nm to 10 μm. Here, the specific surface area is particularly preferably 40 (m ² / g) or more, and the thickness of the thin film is particularly preferably 500 nm or more and 5 μm or less. Further, the metal oxide porous semiconductor film preferably has a surface roughness coefficient of 50 or more, particularly preferably 100 or more. Here, the surface roughness factor R (roughness factor) means the ratio of the actual surface area of the material to the apparent projected area, and this ratio is the specific surface area S (m ² / g) of the material and the electrode substrate of the material. Using the above loading M (g / m ² ), R = SM.

In the photovoltaic layer 3 of the solar cell of the present invention, the photosensitive perovskite compound 32 is physically bonded to the surface of the metal oxide constituting the porous metal oxide, and as the photosensitive perovskite compound, What is represented by the following general formula is used.
CH ₃ NH ₃ M ¹ X ₃ (wherein M ¹ is a divalent metal ion and X is F, Cl, Br, I)

The inorganic framework in the photosensitive perovskite compound of the present invention has a metal halide octahedron layer sharing a vertex. Anionic metal halide layers (eg, [M ¹ X ₆ ] ⁴⁻ ) are generally divalent metals in order to balance the positive charge from the cationic organic layer. Specifically, the metal constituting the anionic metal halide layer of the photosensitive perovskite compound of the present invention is M ¹ (eg, Cu ²⁺ , Ni ²⁺ , Mn ²⁺ , Fe ²⁺ , Co ^2+). Pd2 +, Ge2 ⁺ , Sn2 ⁺ , Pb2 ⁺ , Eu2 ⁺ ).

The halide constituting the anionic metal halide layer of the photosensitive perovskite compound of the present invention is fluoride, chloride, bromide, iodide, or a combination thereof. This halide is preferably bromide or iodide. Specific examples of the perovskite compound include CH ₃ NH ₃ PbI ₃ , CH ₃ NH ₃ PbBr ₃ , (CH ₃ (CH ₂ ) _n CHCH ₃ NH ₃ ) ₂ PbI ₄ [n = 5 to 8], (C ₆ H there are _{5 C 2 H 4 NH 3)} 2 PbBr 4.

  The photosensitive perovskite compound of the present invention can be synthesized by a self-organization reaction using a precursor solution. The film or adsorbent of the photosensitive perovskite compound of the present invention is obtained by dissolving the photosensitive perovskite compound in an organic solvent, then gravure coating method, bar coating method, printing method, spraying method, spin coating method, dip method, die coating method, etc. The coating method can be used.

  In preparing a solution for applying the photosensitive perovskite compound to the surface of the metal oxide porous semiconductor film, the solvent used in the solution is not particularly limited as long as it can dissolve the perovskite. Esters (eg, methyl formate, ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate, pentyl acetate, etc.), ketones (eg, γ-butyrolactone, N-methyl-2-pyrrolidone, acetone, Dimethyl ketone, diisobutyl ketone, cyclopentanone, cyclohexanone, methylcyclohexanone, etc.), ethers (eg, diethyl ether, methyl-tert-butyl ether, diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3- Dioxolane, 4-methyldioxolane, tetrahydrofuran, methyltetrahydrofuran, anisole, phenetole, etc.), alcohols (eg, methanol, ethanol, 1-propanol, 2-propanol, 1 Butanol, 2-butanol, tert-butanol, 1-pentanol, 2-methyl-2-butanol, methoxypropanol, diacetone alcohol, cyclohexanol, 2-fluoroethanol, 2,2,2-trifluoroethanol, 2, 2,3,3-tetrafluoro-1-propanol, etc.), glycol ethers (cellosolves) (eg, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monoethyl ether acetate, triethylene glycol) Dimethyl ether, etc.), amide solvents (eg, N, N-dimethylformamide, acetamide, N, N-dimethylacetamide, etc.), nitrile solvents (eg, acetonitrile, isobutyronitrile, pro Pionitrile, methoxyacetonitrile, etc.), carboat agents (eg, ethylene carbonate, propylene carbonate, etc.), halogenated hydrocarbons (eg, methylene chloride, dichloromethane, chloroform, etc.), hydrocarbons (eg, n-pentane, cyclohexane, n- Hexane, benzene, toluene, xylene, etc.) and dimethyl sulfoxide. These may have a branched structure or a cyclic structure. Two or more functional groups of esters, ketones, ethers, and alcohols (that is, —O—, —CO—, —COO—, —OH) may be contained. The hydrogen atom in the hydrocarbon moiety of the esters, ketones, ethers and alcohols may be substituted with a halogen atom (particularly a fluorine atom).

  The photosensitive perovskite compound of the present invention can be used in combination with other organic or inorganic photosensitive materials. Here, the organic photosensitive material includes many organic dyes used as a sensitizer for dye-sensitized solar cells. These include, for example, ruthenium complexes and iron complexes having a ligand containing a bipyridine structure or a terpyridine structure, porphyrin compounds, phthalocyanine derivatives, eosin, cyanine dyes, merocyanine dyes, coumarin dyes, indoline dyes, oxazole dyes, triphenyl Examples thereof include polymer compounds such as amine dyes, squarylium dyes, oligothiophene derivatives, and polythiophenes. Examples of the inorganic photosensitive material include compound semiconductor nanoparticles such as CdS, CdSe, and PbS, or quantum dots.

  Hereinafter, the structure and the manufacturing method in the solid thin film type organic-inorganic hybrid solar cell of the present invention will be described with reference to examples more specifically showing the above embodiment.

[Example 1]
(1) Production of metal oxide porous semiconductor film A laminated film of tin-added indium oxide (ITO) or fluorine-added tin oxide (FTO) on a glass substrate was used as a transparent electrode (transparent conductive substrate). This surface was sprayed with an acetylacetone solution of titanium isopropoxide and thermally decomposed in air at 200 ° C. or higher to coat a dense thin film of titanium dioxide having a thickness of about 40 nm as a buffer layer. On this thin film, a paste containing nanocrystal particles was applied by screen printing and dried and dehydrated at 200 ° C. for 20 minutes to form a titanium dioxide porous film having a film thickness of about 5 μm. The porous membrane had an average pore diameter of 25 nm and a porosity of about 60%.

(2) Synthesis of photosensitive perovskite compound [CH ₃ NH ₃ PbX ₃ ] In a three-necked flask, 1 g of methylamine [CH ₃ NH ₂ ] and 100 ml of methanol [CH ₃ OH] were placed, and hydrogen iodide was bubbled while performing nitrogen bubbling. Acid [HI] was added to adjust the pH to about 3 to 4, followed by stirring with a magnetic stirrer for 1 hour. This solution was distilled with an evaporator, dried at 40 ° C., and purified again to synthesize methylamine iodide [CH ₃ NH ₃ I]. Next, the synthesized methylamine [CH ₃ NH ₃ I] and lead iodide [PbI ₂ ] are in a molar ratio of 1: 1 to a concentration of 5% by weight in dimethylformaldehyde [(CH ₃ ) ₂ NCHO]. Then, the mixture was dissolved to prepare a dimethylformaldehyde solution of an organic / inorganic hybrid perovskite compound [CH ₃ NH ₃ PbI ₃ ]. Further, dimethylformaldehyde of perovskite compound [CH ₃ NH ₃ PbBr ₃ ] from methyl bromide [CH ₃ NH ₃ Br] and lead bromide [PbBr ₂ ] synthesized from hydrobromic acid [HBr] by the same method. A solution was prepared. Also, by a similar method, a chloride _{[CH 3 NH} 3 PbCl 3]. A perovskite compound in which two kinds of halogens were mixed was also synthesized.

(3) Synthesis of inorganic charge transfer agent perovskite compound [CsSnI ₃ ] Cesium iodide [CsI] and tin iodide [SnI ₂ ] in a molar ratio of 1: 1, dimethylformaldehyde [(CH ₃ ) ₂ NCHO] Was dissolved in 5% by weight to prepare a dimethylformaldehyde [(CH ₃ ) ₂ NCHO] solution of an inorganic perovskite compound [CsSnI ₃ ].

(4) Preparation of Dispersion of Charge Transfer Agent Carbon Nanotubes After commercially pulverizing commercially available single-walled carbon nanotubes (SWCNT) (aspect ratio 50-100), classification is performed, aspect ratio 20-30, average length SWCNTs with a thickness of 1 mm or less were prepared. After this SWCNT was dispersed in a mixed solvent of chlorobenzene and isopropane and sonicated, 2,2 (7,7 (-tetrakis- (N, N-di-methoxyphenylamine) 9, 9 (-spirobifluorene))) (Spiro), a trace amount of an organic surfactant was added and dissolved as a dispersion aid, and the mixture was further dispersed by ultrasonic waves. Here, various liquid dispersions were prepared by changing the weight ratio of SWCNT to Spiro.

(5) Production of photoelectric conversion element A dimethylformaldehyde solution of an organic-inorganic hybrid perovskite compound [CH ₃ NH ₃ PbI ₃ ] is applied at 1500 revolutions on the surface of the titanium dioxide porous film on the transparent electrode using a spin coater. The coating was developed for 2 seconds and dried at 100 ° C. for 30 minutes to form yellow crystals of the perovskite compound [CH ₃ NH ₃ PbI ₃ ] on the surface of titanium dioxide. Similarly, a thin film of a crystal of [CH ₃ NH ₃ PbBr ₃ ], which is bromide, was also formed on the surface of another porous titanium dioxide film. Titanium dioxide film coated with perovskite shows strong band gap absorption in the optical characteristics of perovskite, which is a semiconductor. Especially, in the case of iodide CH ₃ NH ₃ PbI ₃ , visible light extends over a long wavelength up to 800 nm. Almost completely absorbed and showed a black color. These perovskite-coated titanium dioxide thin films were then coated on the surface by spreading the SWCNT dispersion at 2000 rpm for 30 seconds, allowed to stand overnight in the dark and dried to form a thin film comprising SWCNT and Spiro (thickness of about 0 .5 μm). The uppermost layer of these laminated films was covered with a silver thin film (thickness of about 100 nm) as a counter electrode by using a vacuum vapor deposition machine to produce a photoelectric conversion element.

[Example 2]
Instead of Spiro mixed with SWCNT, an inorganic perovskite compound [CsSnI ₃ ] having a photosensitivity in the visible light wavelength range from 450 nm to 700 nm is used. The dispersion of SWCNT and CsSnI ₃ (weight concentration of SWCNT 40%) dispersed by the above is coated with a spin coater on the surface of the titanium dioxide porous film coated with the perovskite compound [CH ₃ NH ₃ PbI ₃ ]. A photoelectric conversion element was produced by the same method as in Example 1.

[Example 3]
In Example 1, soluble magnesium phthalocyanine (MgPc) as an organic pigment having a photosensitivity from a wavelength of 400 nm to 700 nm was further added to a thin film composed of SWCNT and Spiro (weight ratio of SWCNT 40%) to a wavelength of 400 nm to 700 nm with respect to the weight of SWCNT. A photoelectric conversion element was produced in the same manner as in Example 1 except that the added thin film was coated on the surface of the titanium dioxide porous film coated with the perovskite compound [CH ₃ NH ₃ PbI ₃ ] with a spin coater.

The photoelectric conversion characteristics of the solid junction type photoelectric conversion element produced as described above were evaluated. The light receiving area of the cell was set to 0.25 cm ² by a light shielding mask. The tendency for the fill factor (FF) to decrease due to the influence of the internal resistance of the cell increases as the output photocurrent density increases. Therefore, as a light source, a pseudo solar light source in which an AM1.5G filter is attached to a 300 W xenon lamp light source device is used, and an irradiation light amount is set to a strong light amount of 1.5 sun (AM1.5G, 150 mWcm ⁻² ) higher than normal conditions. did. Under this condition, the solid junction photoelectric conversion element manufactured by the above method was connected to a source meter (2400 type source meter, manufactured by Keithley), and the bias voltage was changed from 0V to 0.8V to 0.01V. The output current of photovoltaic power generation was measured while changing the unit, and the FF and energy conversion efficiency were measured.

  Table 1 shows a comparison of photoelectric conversion characteristics of the solid thin film solar cells having different material structures manufactured in the above examples.

  As shown in Table 1, in the solar cell according to the configuration of the present invention, it is apparent that the power generation characteristics of the solar cell are improved by increasing the fill factor and improving the conversion efficiency. As for the photosensitive perovskite compound, a good fill factor (FF) is obtained for both iodide and bromide (cell 8). Since iodide has a wider photosensitive wavelength region than bromide, efficiency is high. In the structure of the carbon nanotube layer that is the charge transport layer, the SWCNT content is in the range of 5% to 50% in the system in which SWCNT and Spiro are mixed with respect to the single-walled carbon nanotube SWCNT alone (100%). Fill factor (FF) and energy conversion efficiency are improved. In addition, even in a system (cell 9) in which CsSnI3, which is an inorganic conductive material and has photosensitivity, is mixed instead of Spiro, good performance is obtained. Further, in the mixed system of WCNT and Spiro, the efficiency of the system (cell 10) in which MgPc having photosensitivity is further added is slightly improved compared to the system in which this is not added (cell 4).

  A photoelectric conversion element comprising an organic-inorganic laminated structure containing carbon nanotubes prepared according to the configuration and production method of the present invention can be formed in a short time by simple solution coating, and is a thin film solid type having excellent photoelectric conversion characteristics The solar cell can be manufactured by a low-cost process.

DESCRIPTION OF SYMBOLS 1 Transparent electrode 11 Transparent substrate 12 Transparent conductive film 2 Counter electrode 3 Power generation layer 31 Metal oxide semiconductor porous film 32 Photosensitive perovskite compound 4 Carbon nanotube charge transport layer 5 Buffer layer

Claims (5)

A metal oxide semiconductor having a nanoporous structure on a conductive substrate, a general formula CH ₃ NH ₃ M ¹ X ₃ (where M ¹ is a divalent metal ion, X is F, Cl, Br , I.) A photoelectric conversion element comprising a photosensitive material having a perovskite crystal structure and a thin layer of a conductive material made of carbon nanotubes, which are sequentially laminated.   2. The photoelectric conversion element according to claim 1, wherein the thin layer of the conductive material made of carbon nanotubes is a conductive organic compound containing carbon nanotubes in a range of 5% to 50% by weight.   2. The photoelectric conversion element according to claim 1, wherein the thin layer of the conductive material made of carbon nanotubes is a conductive inorganic compound containing carbon nanotubes in a range of 5% to 50% by weight.   3. The photoelectric conversion element according to claim 1, wherein the conductive organic compound further includes a photosensitive organic compound having light absorption in a wavelength range of 400 nm to 1500 nm.   4. The photoelectric conversion element according to claim 1, wherein the conductive inorganic compound is a p-type inorganic semiconductor having light absorption in a wavelength range of 400 nm to 1500 nm.